1. Field of the Invention
The invention relates to a pressure regulating valve for regulating the pressure in a high-pressure reservoir of an internal combustion engine, in particular in common rail injection systems.
The invention also relates to a fuel system of an internal combustion engine, in particular of a common rail injection system, as generically defined by the preamble to claim 10.
2. Description of the Prior Art
From German Patent Disclosure DE 10 2005 052 636 A1, a fuel system is known which includes a feed pump that feeds fuel from a fuel tank. From the feed pump, via an adjusting device called a metering unit, the fuel reaches a high-pressure fuel pump, which compresses the fuel and supplies a high-pressure reservoir (“rail”). A plurality of fuel injectors are connected to the high-pressure reservoir. The pressure in the high-pressure reservoir is adjusted, among other ways, by means of a pressure regulating valve (diversion valve). The fuel diverted from the high-pressure reservoir is in general returned to a fuel tank.
The basic function of pressure regulating valves is to enable pressure regulation in the high-pressure reservoir, or rail pressure regulation, in various modes of regulation, and to ensure pressure limitation as a safety function, to preclude risk to humans and the environment. In cases in which there is a control unit or power supply failure, the safety function should still be ensured, in the form of a pressure limitation in the high-pressure reservoir.
From the general prior art, two different types of pressure regulating valves are known for diverting fuel from the high-pressure reservoir and thus for adjusting the pressure in the high-pressure reservoir. These pressure regulating valves are distinguished from one another in that they are either open or closed when without current.
Pressure regulating valves that are open when without current are as a rule used in passenger cars, while pressure regulating valves that are closed when without current are used in utility vehicles.
The pressure regulating valves that are open when without current are designed such that they are actuated by triggering of a magnet coil, so that the pressure in the high-pressure reservoir is adjusted to a desired value by diverting fuel from the high-pressure reservoir. If there is a failure of the control unit or the power supply, the pressure regulating valve is opened, so that fuel is diverted from the high-pressure reservoir. Thus even in failure situations, the safety function of the pressure limitation in the high-pressure reservoir is ensured by the pressure regulating valve. However, the disadvantage of this construction is that when there is a power loss, for instance from cable breakage caused by damage from martens, no further rail pressure can be built up, and the engine or motor will no longer work. Hence an emergency operation function (so-called limp home functionality) is thus unattainable.
In pressure regulating valves for common rail injection systems that are closed when without current, the direction of action is the reverse compared to the pressure regulating valves that are open when without current. In pressure regulating valves that are closed when without current, it is provided that the pressure regulating valve is closed in the currentless state up to system pressure (plus tolerance) via a strong spring. The pressure regulation, that is, the opening of the pressure regulating valve so that pressure can be diverted from the high-pressure reservoir, is effected via a magnet force that acts counter to the closing force of the spring. Supplying current to a magnet coil reduces the closing force of the pressure regulating valve or acts counter to the spring force, as a result of which the pressure in the high-pressure reservoir, or rail pressure, can be regulated to the desired level. In case of a failure, that is, a control unit or power supply failure, rail pressure can thus continue to be built up, and the emergency operation functionality can be ensured.
The safety function of the pressure limitation is intended to be attained by the spring force, in the pressure regulating valves that are closed when without current. The spring force is adjusted to the maximum allowable system pressure in the high-pressure reservoir, optionally plus tolerance. In experiments and simulations, however, it is found that the rail pressure, or the pressure in the high-pressure reservoir, that is established in the currentless state is strongly dependent on the flow rate. In control unit or power supply failures, the system pressure rises, as a function of the flow rate, past the allowable maximum system pressure. This can lead to component damage and can endanger humans and the environment. Moreover, the temperatures in the fuel return of the pressure regulating valve rise to values over 200° C.